1. Field of the Invention
This invention relates to a composition for urethane foam excellent in fire retardancy, impact resistance and heat resistance.
2. Description of the Prior Art
Urethane foams have heretofore been produced by foaming in a open mold a composition comprising as the main constituents one or more isocyantes, polyols and blowing agents.
In recent years, a reaction injection molding technique (RIM technique) has been developed, and urethane foam with a high density skin layer and a low-density core layer (inside layer) is molded by a one-shot process.
However, the urethane foam produced by either of the above-mentioned methods is flammable.
In order to impart fire retardancy to urethane foam, there is known a method by which a halogen-containing organic compound and an antimony oxide are incorporated thereinto.
However, urethane foam given fire retardancy by this method has (a) a tendency to be greatly deteriorated in mechanical properties, particularly impact resistance, and (b) a tendency to be deteriorated in heat resistance. Particularly when urethane foam with a skin layer is produced by RIM method, the urethane foam has, besides the above (a) and (b), (c) a tendency to be deteriorated also in mechanical properties other than impact resistance because voids are apt to be formed in the skin layer and the cells become ununiform in the inside layer.